Almost venerate a large naval officer (7)
I believe the answer is:
admiral
'naval officer' is the definition.
(commander of a naval fleet)
'almost venerate a large' is the wordplay.
'almost' means to remove the last letter (almost the whole word is kept).
'venerate' becomes 'admire' (I've seen this in another clue).
'large' becomes 'L' (eg in clothes sizes).
'admire' with its last letter removed is 'admir'.
'admir'+'a'+'l'='ADMIRAL'
(Other definitions for admiral that I've seen before include "(White or red) butterfly" , "foremost in fleet" , "Naval officer of high rank" , "Naval high-up" , "[NELSON] perhaps" .)